Recently, by the appearance of the refrigeration air conditioning system and heat pump system using the two-phase flow ejector, the efficiency of the cycle has been largely improved in comparison with the conventional system. In mixing section of the ejector, the suction flow of the subsonic single-phase gas refrigerant flows through the outside of the driving flow of the supersonic two-phase refrigerant. Within these flow fields, shock and expansion waves that affect the performance of the ejector can occur; therefore, such effects must be taken into account in the design of the ejector system. In this study, the expansion waves generated in flow fields with different speeds of sound are researched analytically by changing the momentum and thermal relaxation times. From analysis results, we successfully made expansion waves which occur in the flow field with two-phase flow and single phase gas flow, even though single-phase gas flows were subsonic. The reason, why expansion waves exist in subsonic state is due to the relaxation phenomena between the phases and the pseudo-like-convergent nozzle effect in the single-phase gas flow. The results of this study provide a clue that can help us better understand fluid flow phenomena in the mixing section of the ejector.

Gasoline engines have been required to improve the thermal efficiency and reduce the pollutant emission, and the previous studies were developed by controlling the ignition timing and keeping the constant air-fuel ratio. For further improvement of the thermal efficiency, it is expected to reduce the pressure fluctuations due to the combustion per cycle, which causes to generate the stable combustion field and improve the fuel consumption. Since the pressure fluctuations due to the combustion are significantly affected by the ratio of the residual gas in the cylinder, the present study proposed the method to estimate the ratio of the residual gas, which is defined as the mass ratio of the residual gas and the air-fuel mixture into the cylinder, by using the combustion pressure, and developed the methods to reduce the pressure fluctuations considering the ratio of the residual gas by controlling the ignition timing. Under the experimental condition of the large ratio of the residual gas, it was found that the fluctuations of the indicated mean effective pressure was reduced to more than 20% by using the developed methods.